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25
26 // This file contains the implementation of the ComputeFeatureLookAt function.
27
28 #include "kml/engine/feature_view.h"
29 #include "kml/base/math_util.h"
30 #include "kml/dom/kml_factory.h"
31 #include "kml/engine/bbox.h"
32 #include "kml/engine/location_util.h"
33
34 using kmldom::LookAtPtr;
35 using kmldom::KmlFactory;
36 using kmldom::FeaturePtr;
37
38 namespace kmlengine {
39
40 // The range of the LookAt that emcompasses the feature's extents depends on
41 // the field of view of the virtual camera. Google Earth has a 60 degree
42 // horizontal FOV (equivalent to looking through a 30mm lens) and that value
43 // is used here.
44 static const double kFieldOfView = 60.0;
45
46 // To avoid zooming in to far to point features or features that are spatially
47 // small, we clap the computed range to a minimum value. Google Earth has
48 // always used 1 km as its minimum.
49 static const double kMinRange = 1000.0;
50
ComputeFeatureLookAt(const FeaturePtr & feature)51 LookAtPtr ComputeFeatureLookAt(const FeaturePtr& feature) {
52 Bbox bbox;
53 if (!GetFeatureBounds(feature, &bbox)) {
54 return NULL;
55 }
56 return ComputeBboxLookAt(bbox);
57 }
58
ComputeBboxLookAt(const Bbox & bbox)59 LookAtPtr ComputeBboxLookAt(const Bbox& bbox) {
60 // The distance from the center point to the northern bound.
61 const double d_north = kmlbase::DistanceBetweenPoints(
62 bbox.GetCenterLat(), bbox.GetCenterLon(),
63 bbox.get_north(), bbox.GetCenterLon());
64 // The distance from the center point to the western bound.
65 const double d_west = kmlbase::DistanceBetweenPoints(
66 bbox.GetCenterLat(), bbox.GetCenterLon(),
67 bbox.GetCenterLat(), bbox.get_west());
68 // The distance from the center point to the north-western bound.
69 const double d_nw_corner = sqrt(pow(d_north, 2) + pow(d_west, 2));
70 // Scale the result by 1.2 to provide a margin around the feature.
71 double range = d_nw_corner * tan(kmlbase::DegToRad(kFieldOfView)) * 1.1;
72 if (range < kMinRange) {
73 range = kMinRange; // Clamp to minimum range.
74 }
75 LookAtPtr lookat = KmlFactory::GetFactory()->CreateLookAt();
76 lookat->set_longitude(bbox.GetCenterLon());
77 lookat->set_latitude(bbox.GetCenterLat());
78 lookat->set_range(range);
79 lookat->set_altitudemode(kmldom::ALTITUDEMODE_RELATIVETOGROUND);
80 // We don't explcitly set the altitude, tilt or heading, relying instead on
81 // their defaults of 0. This produces a LookAt that is north-up, looking
82 // straight down.
83 return lookat;
84 }
85
86 } // end namespace kmlengine
87